1. Field of the Invention
This invention relates generally to rotating electrical machines such as electric motors and generators, and more particularly to apparatus for detecting and indicating bearing failure.
2. Description of the Prior Art
Rotating electric machines are common in industry. Electric motors are widely used for driving a great variety of machinery. Many such motors fail prematurely, due to improper maintenance, particularly a failure to maintain lubrication of bearings.
The above mentioned problem has existed for many years. Various means have been devised for sensing and indicating impending or existing bearing failure. The U.S. Pat. Nos. 3,508,241 and 4,074,575 disclose such apparatus incorporated directly in bearings. In the earlier of these two patents, there is an auxiliary bearing to assist in handling the load upon failure of the main bearing, and the sensing and indicating device is intended to operate at the same time. The incorporation of supplementary or reserve bearings, and an alarm which is activated upon transfer of the load to such bearings when a main bearing fails, can also be found in U.S. Pat. Nos. 3,452,349 and 4,063,786.
A different approach for detecting bearing wear can be found in U.S. Pat. No. 4,107,603 where the displacement of a shaft-engaging sensor, in a direction transverse to the shaft, is used to create a signal for use in determining excessive shaft movement which may result from excessive bearing wear.
An approach using thermocouples is found in U.S. Pat. No. 3,582,928. A pair of proximity probes at 90 degrees with respect to each other and to the shaft axis, is used in U.S. Pat. No. 3,678,493. Capacitive effects in apparatus employing gas bearings are found in U.S. Pat. No. 3,176,286. Inductive effects are employed for bearing wear detection in a pump in U.S. Pat. No. 3,981,621 and in bearing protection for a generator, in U.S. Pat. No. 3,373,300. In the latter, sensor coils are disposed in stator slots at 180 degrees with respect to each other, and voltages resulting from uneven clearance between the rotor and the two sensor coils are utilized to generate a signal indicating a bearing failure.
Most of the aforementioned devices require special kinds of bearings or installation and do not appear to be readily retrofitted to existing conventional motors or generators. The above mentioned patent, U.S. Pat. No. 3,373,300 to Sullivan, may be, the most readily utilized in a conventional motor or generator.